1. Field of the Invention
The invention relates to a method for determining a sprinkler water delivery requirement to control a fire. The invention also relates to an apparatus for measuring heat flux, especially in connection with fire protection, the fire testing of materials, and determining a sprinkler water delivery rate.
2. Background of the Invention
The fire hazard represented by storage of a given material is often characterized by the rate of delivered sprinkler water required to suppress or control a fire of that material. The present state-of-the-art for hazard characterization is to perform replicate tests in which: the material is ignited; the fire is allowed to grow until it is sensed by sprinklers; and the sprinklers then activate to deliver water to the fire. The delivered water density, that is, the amount of water delivered by the sprinklers per unit area of the floor, is systematically increased until a delivery rate that controls the fire is found. Many standard tests must be performed with the same material to determine what rate of sprinkler water delivery is required to control the fire from the burning material. These replicate tests consume a great deal of personnel labor and material, and are thus very expensive and time-consuming.
The severity of fires and the hazards they present are assessed in terms of the total chemical heat release rate of the fire and the heat flux emitted. Heat flux is defined as the rate of energy transfer per unit surface area. Heat flux is typically expressed in units of kilowatts per square meter or BTU per square foot per minute. The measurement of heat flux is of importance in many sciences, including the fire testing of many materials. The heat flux emitted by burning materials may ignite, or aid in the burning of, nearby materials. In one known test set up, a gas burner is positioned at the base of and between two parallel panels on which a test material, for example, a fire resistant material such as polyurethane insulation, is placed. Measurement of heat flux in this parallel panel test provides valuable information about the response of the test material to the flames from the burner.
Instrumentation presently available for measuring heat flux requires complex, time-consuming installation, and is not sufficiently robust to withstand repeated use in very severe fire environments. The conventional instrumentation usually consists of water-cooled heat flux gauges that need to be individually installed, for example, directly on the panels bearing the test material. These gauges are exposed to flames during use. Individual heat flux gauges must undergo time-consuming calibration before and after the test because their sensing elements are easily damaged or impacted by fire impingement and by the deposition of soot and other incomplete products of combustion. A measurement uncertainty arises when post-test calibration shows that the gauge calibration constant has shifted as a result of this impact. Moreover, the gauges are individually water-cooled and mounted to view the flames through openings drilled in the material and supporting structure. This adds time and expense to the testing program and severely limits the number of heat flux measurement stations that can be installed. In some fire test configurations, such as commodity classification, it is not practical to install heat flux gauges due to the difficulty of protecting water cooling lines and electrical connections in highly hazardous locations.